Long post warning:
I've driven hybrids since 2008 (all Toyotas). Unless you're getting directly on the highway and not stopping ever at all until you get to your destination, and never just driving to the store or a restaurant - or whatever - then you're doing some mixed driving. Even if you ONLY drive on interstates at high speed, and never have to idle in traffic or stop at signal lights, your mileage is still going to depend on altitude and temperature and the weight your carrying.
My current car sits pretty firmly at an average mpg of 52.4 to 52.6. I live in the very flat, low altitude, moderate weather mid-Atlantic coastal area. I drive on highways a lot. I also drive in town a bit. And sit in super annoying traffic sometimes. I don't carry much load except when it's my turn to drive the 4 adults to the big city for college basketball games (maybe once a week during the season).
So that's what I do, and I get 52.4 mpg doing it in a car that's EPA rated at 50 mpg city/48 highway, I think.
Last week, I loaded my husband, his recumbent touring bicycle, bike rack, camping gear, a filled 35 quart cooler, luggage, bike tools, big ass first aid kit, and a full tank of gas, and transported all that crap uphill to the mountains of NC, some 290 miles away. My gas mileage for that trip was 44.9. I spent the week working my way back in a generally downhill direction - minus husband and bike - while my husband cycled the Mountains to Coast Ride. (He rides; I report/blog about it.)
By the time we made it to the beach on Saturday, my 'trip' mileage was 49.6 mpg, and my Life of Car mpg was at 51.2 mpg.
tl;dr: The Maverick has a bigger hybrid battery, but weighs more. I would expect it to get about 8% better mpg than predicted in ideal driving environments and maybe 5% less than predicted under more extreme driving environments. Either way, it's better than anything else on the market.
